I am studying the AXI4 version H_c specification. I do not understand the content of the chapter "A6: AXI Ordering Model".
In particular, "A6.4 Observation and Completion Definitions" is difficult to understand. The word observation is too abstract for me. I think that a transaction is either a command or data. This specification states that a transaction is observing another transaction. I don't understand the mean of the word.
Please tell me what this word means for a transaction, and what part of AXI it applies to.
The term is used in descriptions of a memory-ordering model. The A6.4 section defines the term 'observe'. Therefore, when reading the document one must rely on that particular definition of the term to understand the statements. Some other literature (for e.g. those that describe the memory ordering model for POWER CPUs) uses 'performed' to mean 'observe'. In any case, these are terms whose names are not as important as what they define.
Have you checked the armv8 memory model in the arm manual, and also the "Transfer behavior and transaction ordering" section of this document?